Synthesis of Ni-doped InTaO_4 nanocrystallites by reactive pulsed laser ablation for application to visible-light-operating photocatalysts

摘要

Ni-doped InTaO_4 nanocrystallites were synthesized by a reactive pulsed laser ablation process, aiming at visible-light-operating photocatalysts. The third harmonics beam of a Nd:YAG laser was focused onto a sintered In_(0.9)Ni_(0.1)TaO_(4-δ) target in mixture background gases (O_2 + He). The deposited species were columnar-structured porous films consisting of primary nanocrystallites. The mean diameter of the primary nanocrystallites was 4 nm. Optical absorption characteristics, especially in low absorbance (sub-band) regions, were evaluated by photoacoustic spectroscopy. Absorption in the sub-band region decreased drastically with increasing O_2 partial pressures. It is inferred that oxygen deficiencies are suppressed, because of enough oxygen vapors in the reactive background gases. An absorption band around 420 nm appeared obviously in O_2 partial pressures above 5%, in the Ni-doped InTaO_4 nanocrystallites. The visible region absorption band is presumably attributed to the Ni 3d-eg orbitals. In contrast, pure InTaO_4 nanocrystallites showed a sharp band edge, without the visible absorption band.